Electrical protective system



K. L. MAURER El AL.

ELECTRICAL PROTECTIVE SYSTEM Filed Aug. 1, 1936 lNVENTORS fi fllfSwam ATTORNEY Dec. 28, 1937.

Patented Dec. 28, 1937 UNITED STATES PATENT OFFICE ELECTRICAL PROTECTIVE SYSTEM Keith L. Maurer, Rockville Centre, N. Y., and

Leland K. Swart, Mountain Lakes, N. J., assignors to American Telephone and Telegraph Company, a corporation of New York Application August 1, 1936, Serial No. 93,910

4 Claims. (Cl. 175-294) This invention relates to voltage-limiting detacle takes place and the resistance between the vices for electrified railways. It further relates main electrodes is rapidly lowered to the extent to electrical protective systems and more parthat current is permitted to flow between them, ticularly to arrangements for simultaneously conthus more or less effectively short-circuiting the 5 necting in parallel or grounding a plurality of conductors to which these electrodes are conrailway tracks when voltages above a predeter nected. The voltage drop across the established mined value become impressed on one or another arc will be approximately 15 volts and is subof railway tracks. stant-ially independent of the current. After In the course of operation of one or more termination of the disturbance producing ignirailway tracks there may occur periods of short tion voltage, ionization ceases in the receptacle l0 circuit or excessive load on the electrification and the insulation between the various structures system associated with the tracks. At such times is restored. the voltage that may exist between the tracks Referring more specifically to Fig. 1, T1, T2, and the ground may be e ces and this T3 and T4 represent the tracks, each track in vention relates specifically to an arrangement general comprising two rails. A mercury vapor 5 for limiting that voltage. Briefly the limitation device P1 contains a pool of mercury, which is of voltage to ground is effected by short-circuitgrounded at G. An igniting electrode E, which ing the Tails to eac o e r o ground for the connected to the tracks to be protected through duration of the disturbance producing the unbridged resistances or reactances or similar coudesired voltage. The limitation of these voltpling arrangements Z1, Z2 and. Z3, dips into the ages under abnormal conditions may frequently mercury pool as shown in the figure. This ig- 20 be desired from the standpoint of electric shock nition electrode E is preferably of high resistive hazard, particularly in the vicinity of passenmaterial such as thyrite, carborundum or other ger station platforms. Such interconnection of refractory material which possesses some contracks and conductors in parallel therewith durductivity. In addition each track is connected 5 ing abnormal conditions also will be generally by conductors I, 2, 3 and 4 to a separate currentadvantageous from the standpoint of the rccarrying anode in the receptacle, these anodes duction of inductive effects produced by the asbeing preferably symmetrically situated with resociated currents in the electrification system. spect to the mercury pool, which latter serves h i ti l be b tt understood by as a cathode connected to a low resistance 30 reference to the following specification and the ground a ground Wire, as Shown at In accompanying drawing in which Figure 1 shows the event that a short circuit occurs on any one an arrangement applicable to D electrifica- Of tracks. the voltage 021 the igniter E is suftion; Hg 2 shgvjs an arrangement adapted f r ficient to produce an initial ionization which imeither A. c. or D. c. electrification systems, with l fi the tube w ionization d 35 reference particularly to two tracks; and Figs. (111093 the resistance between the mercury D 3 t 6 h a i i arrangement appucabie to and the anodes to such an extent that all of the a larger number of tracks. tracks are immediately short-circuited to ground. the devices Shown with the Various figures, This short circuit is maintained as long as the the same principle is used in all and they diffe disturbing voltage persists, and upon its cessa- 40 only in the details of their application. More tion deionization the tube Occurs and the particularly use is made of an insulated tracks are restored to a normal condition. ceptacle containing one or more pooIs f In view of the characteristics of the mercury wry equipped with igniting electrodes Ashort tube. it will be evident that this arrangement 5 circuit occurring on one of the tracks in the will be efifective only in the event that one of the cinity of the point of connection of the device tracks becomes positive with respect to ground will produce a difference in potential between and then only if its pfl e dS that 01' that track and ground and between that track ground pot y Certain Value deter ined and the remaining tracks and conductors, such by the design 0f the mercury Vapor deViCe- A150, as ground wires, in parallel therewith. This dif- 1. 2. v been sp of s a h in 50 ference in potential is impressed upon the ignita track With tWO rails- Actually 1 y be ing electrode and after an interval, dependin one rail and T2 the other rail of a track. upon the design of the apparatus and the min- Fig. 2 shows an arrangement for application to imum voltage for which operation is desired, either an A. C. or a D. C. system by virtue of an ionization of the mercury vapor in the recepinterconnection in the structures involved. Thus 55 with an igniting electrode.

P2 comprises an insulated receptacle containing two mercury pools, each with an igniter electrode. Each pool is connected with one rail of a track and the igniter for that pool is connected to the other rail of the two shown in Fig. 2. Thus the rail T1 is shown as having a connection to one mercury pool and a connection to the igniter electrode of the other mercury pool. So, also, for rail T2. In the event of a short circuit to one of the rails or structures to which the device is connected, a difference in potential is set up between that structure and the other. This potential difference, being impressed upon the corresponding igniting electrode, produces ionization of mercury and a consequent breakdown of resistance between the two mercury pools, thus bringing the rails T1 and T2 to substantially the same potential. T1 and T2 may each represent a track of two rails in which case the rails would be bridged by impedances such as Z1, etc., of Fig. 1.

The same explanation holds for Figs. 3, 4 and 5 which show respectively protection for 3, 4 and 5 tracks. The protection device consists in each case of an insulating receptacle which contains a mercury pool for each track or other conductor to be protected, and each mercury pool is equipped With this arrangement a short circuit to any one of the tracks or structures initiates ionization in the mercury receptacle which spreads throughout the receptacle, thus short-circuiting all the tracks to each other and connecting them virtually in parallel for the duration of the disturbance. In case there is a ground wire or system of ground wires, and it is desired to short-circuit the tracks to this ground wire during the period of disturbance, then that ground wire or system of ground wires takes the place of one of the tracks as shown in a Fig. 5.

The arrangement of Fig. 6 is a refinement applicable to A. C. or I). C. electrification systems and specifically employs a substantial system of ground conductors GW. In this arrangement the receptacle, as in the previous cases, is provided with a mercury pool for each track. Here the two rails of any one track are shown separately and bridged by a suitable impedance such as Z1, of such character that it does not interfere with normal track signaling. Each track is shown as connected from a midpoint of its bridging impedance to one of the mercury pools. An additional mercury pool is provided for the ground wires. Each of the pools connected to the tracks is providedwith an igniting electrode, all of these electrodes being connected to the ground wire. At the same time the pool connected to the ground wire contains a plurality of igniting electrodes, one for each track to be protected, and connected to that track. With this arrangement it is apparent that ignition will occur in the event of excessive potential on any one of the tracks of either a positive or a negative value and, as a result of the initial ionization thus produced, all of the tracks will be short-circuited to the ground wire for the duration of the disturbance.

It has been found, experimentally, that in an electrification system containing a number of tracks and a substantial ground wire system, a short circuit on one track may produce a substantially larger difference in potential between that track and the ground wire system than between that track and any of the other tracks.

In all of the arrangements shown the tracks are permanently interconnected through the igniting electrodes. These electrodes, however, are confined to materials possessing a high initial resistance. Thus no difliculty is presented in designing the apparatus so that it will not interfere with track signals.

While this invention has been described in connection with a limited number of tracks or parallel conductors, it is evident that it may be arranged to accommodate any number of such tracks or conductors and will provide protection against any desired voltage to ground, within reasonable limits.

What is claimed is:

1. In a protective circuit for an electrical system including two substantially parallel conductors and including means for short-circuiting the two conductors together when excessive voltage is applied to one, the combination of an insulating vessel with two adjacent mercury pools, a low resistance connection from each conductor to one of the pools, an igniter electrode for each pool, and a connection from the igniter electrode of one pool to the conductor connected to the other pool.

2. In a protective circuit for an electrical system including a plurality of parallel electrical conductors and including means for short-circuiting all the conductors together when excessive voltage is applied to one, the combination of a containing vessel with a plurality of adjacent mercury pools, one for each conductor, a low resistance connection from each conductor to one of the pools, an igniter electrode for each pool, and a connection from each igniter electrode to one of the conductors other than the one to which its pool is connected.

3.. In a protective circuit for an electrification system, the combination of a plurality of conductors subject to excessive disturbing voltages, one of the conductors being a grounded wire system, means for short-circuiting these conductors to each other and to ground during the period of disturbing voltages, said means comprising an evacuated vessel, a plurality of separate mercury pools in the vessel, one for each conductor to be protected and one for the ground connection, connections from the conductors and ground to their respective mercury pools, an igniter electrode as sociated with each mercury pool, and a connection from each igniter to a conductor other than the one to which its pool is connected.

4. The combination of claim 3 characterized by the fact that there are a plurality of igniter electrodes for the grounded pool, and a connection from these to each conductor to be protected whereby an excessive voltage on any one conductor will short-circuit all the conductors to ground.

KEITH L. MAURER. LELAND K. SWART. 

